From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A544D230994 for ; Tue, 12 Nov 2024 19:02:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731438174; cv=none; b=FOJDX/NHAF7HuuTyZd3p8OT+fu1xo4/Yy/kYrT+2L7hQvZFkH9rRIapB78WwHXNGPAK0f+yyY3ihUC9QNv8NM4gkwzK0WANTymAV06mzfHk1Pk9od2Oy9gZf8sKPyz5bus3tbbMv09axCUxhTPC4AgN8rfBcv1i6BL9nqZst1ko= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731438174; c=relaxed/simple; bh=bXQK6+F9U+3y68nQst8utZuX1+MTQHrxjDYqgLbuL7o=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=KVFEloGD6fu/iIfsjoFLyxhkv27Dfst0iYE3ZiZJPo+CbSwosITXpcnongjGB4wh1Vup0McMGLRwbzloyF9NavoPW4VbkNZ57XSY1d8DYpdqRk5sS5XFGwy0Vhc1wNcysJnCcv0HEeLMDzDvkYi7cIQV23PIKLeVMdHiYWrO8zw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=N07ZiG6n; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="N07ZiG6n" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65815C4CECD; Tue, 12 Nov 2024 19:02:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1731438174; bh=bXQK6+F9U+3y68nQst8utZuX1+MTQHrxjDYqgLbuL7o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=N07ZiG6nj9Rpu1nLN/5IAmAcVxWUJYJ0rv3khYomgvONZT7kCdMFS3gd3zlos1A1m VSiCUPrCAscYxwYZX+E5yZdtUEz69A3pTjzulNqDPlhNsfozkjqZWHFjmh0Zi57UH4 z2voXs5bfLVGVsG4eQIr6vBRKz7jvFaScIeXB9VliyhtwjtHvzFCTjUNB1RKA2+Qpw dASbCYt9tegbygWniqp+r1hfcCUh6RJVn40rI+jgaGnPQupLoE4HvkCjgutBI4c1Ds Xp57GmCF2KEGg53t+rXzpVK8gknWuKPc1aiDezTmmMxD5ZHrZ9uPfcmQUmjkse0n1H 2TyjVqPJwEM3A== Date: Tue, 12 Nov 2024 09:02:53 -1000 From: Tejun Heo To: Sebastian Andrzej Siewior Cc: Boqun Feng , Hillf Danton , "Paul E. McKenney" , Marco Elver , linux-kernel@vger.kernel.org, gregkh@linuxfoundation.org, tglx@linutronix.de, syzbot Subject: Re: [PATCH] kernfs: Use RCU for kernfs_node::name lookup. Message-ID: References: <66a745bb-d381-471c-aeee-3800a504f87d@paulmck-laptop> <20241102001224.2789-1-hdanton@sina.com> <20241108100503.H-__545n@linutronix.de> <20241108222406.n5azgO98@linutronix.de> <20241111170450.mUxDpLiW@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20241111170450.mUxDpLiW@linutronix.de> Hello, Sebastian. Sorry about late reply. Have been sick for a bit. On Mon, Nov 11, 2024 at 06:04:50PM +0100, Sebastian Andrzej Siewior wrote: ... > Let me check if I understood. We have three users of kernfs: > > - cgroup > cgroup1_rename(): parent check (would get the new KERNFS_ROOT flag) > > - resctrl > rdtgroup_rename(): seems to allow any "mon group" directory > different parent possible. > > - sysfs > sysfs_move_dir_ns(): reame to a different parent I'm not sure about resctrl but here we just need to add that flag to cgroup, right? > That new RCU interface would be used by cgroup only and sysfs/ resctrl > would remain using the "old" code? > If so, would you prefer > |struct kernfs_node { > | … > | union { > | const char name; > | const char __rcu *name_rcu; > | } > > to avoid patching resctrl + sysfs for for the rcu_derference name > lookup? As replied on the patches, it probably is cleaner to always use __rcu and apply the additional locking on the reader side if renaming across different parents is allowed. Thanks. -- tejun